A CO2 purification device and method

Abstract

The application provides a CO2 purification device and method, relates to the technical field of gas separation and purification, and the device comprises a first flash separation device, a heat exchanger, a first compressor, a refrigerating unit, a rectifying tower, an evaporator and an expander; a gas phase outlet at the top of the first flash separation device is communicated with the inlet of the expander, a liquid phase outlet at the bottom of the first flash separation device is communicated with the inlet of the first compressor, the outlet of the first compressor is communicated with the inlet end of the refrigerating unit, the outlet end of the refrigerating unit is communicated with the upper portion of the rectifying tower, the liquid phase outlet at the bottom of the rectifying tower is communicated with the evaporator, the gas phase outlet at the top of the evaporator is communicated with the lower portion of the rectifying tower, and the liquid phase outlet at the bottom of the evaporator is used for discharging CO2 liquid products. The application has the characteristics of low energy consumption and small circulating water consumption, and is suitable for liquefaction and purification of low-purity CO2 flue gas mixture after S / N / Hg integrated removal technology is adopted on oxygen-enriched combustion flue gas.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of gas separation and purification, in particular to a CO2 purification device and method. BACKGROUND

[0002] Oxy-combustion is a technology for capturing, utilizing and storing carbon dioxide in combustion, and the concentration of CO2 in dry flue gas can be as high as 70% to 90% in theory, which is convenient for compression and separation of CO2. The impurity gases in oxy-combustion flue gas are mostly nitrogen, and also contain a small amount of water, oxygen, argon, sulfides, nitrogen oxides, mercury and other pollutants. These pollutants and impurity gases seriously affect the transportation, utilization and storage of CO2, and need to be purified and removed.

[0003] The S / N / Hg integrated removal technology utilizes the compression process of oxy-combustion flue gas to achieve the simultaneous removal of SO2, NO x and Hg; this integrated removal technology can effectively utilize the energy in the compression process, does not need to install traditional desulfurization and denitrification devices, and can recover sulfuric acid and nitric acid products and simultaneously remove Hg, thereby reducing the operating cost of oxy-combustion and being widely accepted. However, after the pollutants in the oxy-combustion flue gas are removed by the integrated removal technology and the flue gas is dried and dehydrated, the obtained CO2 flue gas mixture still contains impurities such as nitrogen, oxygen and argon, and the purity of CO2 is not high, which needs to be further purified.

[0004] The traditional CO2 purification and liquefaction device pre-cools and liquefies the raw gas through a refrigeration cycle system, then throttles to a certain pressure to enter the rectification tower for rectification, the rectification tower is provided with a condenser at the top and a reboiler at the bottom, and CO2 liquid product can be obtained at the bottom of the reboiler, and the light component gas at the top of the rectification tower is vented after recovering cold energy. The traditional CO2 purification and liquefaction device has a high requirement for the CO2 content in the raw gas, and generally speaking, the CO2 content in the raw gas treated by the traditional CO2 purification and liquefaction device is generally above 98% (volume fraction). However, after the pollutants in the oxy-combustion flue gas are removed by the above-mentioned integrated removal technology and the flue gas is dried and dehydrated, the obtained CO2 flue gas mixture has a low CO2 content, which is not suitable for the traditional CO2 purification and liquefaction device.

[0005] In order to deal with the above situation, the patent document with the publication number CN202547276U discloses an oxygen-enriched combustion flue gas CO2 purification and liquefaction device. After purification and liquefaction by the device, the purity of the CO2 liquid product is about 96% (volume fraction), and the product purity is not very high. In order to obtain a CO2 liquid product with a higher purity of more than 96%, an external refrigeration unit refrigeration process is generally used for direct rectification separation, but the overhead condenser of this method needs the refrigerant of the refrigeration unit to provide a lower temperature (-60℃) to produce overhead reflux liquid, and the energy consumption is relatively high.

[0006] In addition, the current purification device does not utilize the waste gas, and there is a waste of waste gas heat energy.

[0007] Therefore, it is of great practical significance to study a method for separating and purifying CO2 from oxygen-enriched combustion flue gas, obtaining a CO2 liquid product with higher purity and higher yield, and consuming less energy.

[0008] The information disclosed in this BACKGROUND section is only intended to enhance the understanding of the general background of the application and should not be considered as recognition or suggestion that this information forms the prior art known to those of ordinary skill in the art. SUMMARY

[0009] In view of the above situation, the present application provides a CO2 purification device and method, which aims to separate and purify CO2 from oxygen-enriched combustion flue gas with lower energy consumption and make full use of waste gas.

[0010] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0011] In a first aspect, the present application provides a CO2 purification device, which can mainly include a first flash separator, a heat exchanger, a first compressor, a refrigeration unit, a rectification tower, an evaporator and an expander.

[0012] The middle part of the first flash separator has a raw gas inlet, the gas phase outlet at the top of the first flash separator is in communication with the inlet of the expander, the liquid phase outlet at the bottom of the first flash separator is in communication with the inlet of the first compressor, the outlet of the first compressor is in communication with the inlet end of the refrigeration unit, the outlet end of the refrigeration unit is in communication with the upper part of the rectification tower, the liquid phase outlet at the bottom of the rectification tower is in communication with the evaporator, the gas phase outlet at the top of the evaporator is in communication with the lower part of the rectification tower, and the liquid phase outlet at the bottom of the evaporator is used to discharge CO2 liquid product.

[0013] In some embodiments of the present application, the upper part of the rectification tower is not provided with a condenser; the raw gas stream first passes through the heat exchanger for cooling and liquefaction, and then enters the raw gas inlet; the stream of the liquid phase outlet at the bottom of the first flash separator first passes through the heat exchanger for reheating, and then enters the compressor; and the stream of the outlet of the first compressor first passes through the heat exchanger for cooling, and then enters the rectification tower.

[0014] In some embodiments of the present invention, the vapor outlet at the top of the distillation column is connected to the feed gas inlet;

[0015] The vapor stream from the top of the distillation column flows through the heat exchanger.

[0016] In some embodiments of the present invention, the raw material gas stream first flows through the evaporator and then enters the raw material gas inlet.

[0017] In some embodiments of the present invention, the CO2 purification apparatus further includes a second flash separator and a second compressor;

[0018] The gas phase outlet at the top of the second flash separator is connected to the feed gas inlet, the liquid phase outlet at the bottom of the second flash separator is connected to the inlet of the second compressor, and the outlet of the second compressor is connected to the upper part of the distillation column.

[0019] In some embodiments of the present invention, the outlet of the first compressor is connected to the inlet of the second compressor.

[0020] In some embodiments of the present invention, the upper part of the distillation column is not equipped with a condenser.

[0021] In some embodiments of the present invention, a first throttling valve is provided on the liquid phase outlet stream at the bottom of the first flash separator, and the first throttling valve is located inside the cold box.

[0022] In some embodiments of the present invention, the CO2 purification device further includes an exhaust gas heater;

[0023] The inlet of the exhaust gas heater is connected to the gas phase outlet at the top of the first flash separator, and the outlet is connected to the inlet of the expander.

[0024] Secondly, the present invention provides a method for purifying CO2, which mainly includes the following steps:

[0025] The raw gas obtained after compression and drying is first pre-cooled by an evaporator, then cooled and liquefied by a heat exchanger, and then sequentially passed through a second flash separator, a first flash separator, a first compressor, a second compressor, and a refrigeration unit. After being cooled and liquefied by the refrigeration unit, it enters the upper part of the distillation column. The liquid stream from the liquid phase outlet at the bottom of the distillation column enters the evaporator, and CO2 liquid product is obtained from the liquid phase outlet at the bottom of the evaporator.

[0026] in:

[0027] After the feed gas enters the evaporator, it acts as a heat source to heat the liquid stream from the liquid phase outlet at the bottom of the distillation column. Part of the liquid from the liquid phase outlet at the bottom of the distillation column is evaporated and then enters the distillation column as rising gas.

[0028] The pressure of the compressed raw material gas is 30 bar;

[0029] The second flash separator separates the liquid phase and the gas phase at a temperature of -24℃, the separated liquid phase is throttled and refrigerated by a first throttle valve, then flows through a heat exchanger for reheat, and then enters the second compressor;

[0030] The first flash separator separates the liquid phase and the gas phase at a temperature of -54℃, the separated liquid phase is throttled and refrigerated by a second throttle valve, then flows through a heat exchanger for reheat, and then sequentially passes through the first compressor and the second compressor; the separated gas phase is heated by the heat exchanger and the waste gas heater, and then enters the expander;

[0031] The stream compressed by the second compressor is pre-cooled by the heat exchanger, then cooled and liquefied to -10℃ by the refrigeration unit, and then enters the upper part of the rectification tower for rectification;

[0032] The stream from the gas phase outlet at the top of the rectification tower is reheated by the heat exchanger, and then enters the evaporator together with the raw material gas.

[0033] Compared with the prior art, the embodiment of the present application has at least the following advantages or beneficial effects:

[0034] 1. After the low-purity CO2 flue gas mixture is compressed and dried, part of the pollutants and water are removed, thereby forming the raw material gas, the raw material gas is cooled and liquefied by the heat exchanger, then flash-separated by the first flash separator, so as to complete the preliminary separation of N2, Ar, O2 and other gas impurities from CO2, then compressed by the first compressor, and finally rectified and purified by the rectification tower without a condenser at the top under the condition close to normal temperature (about -10℃), thereby obtaining the CO2 liquid product with a volume fraction of about 99.99%; the present application combines the flash separation, compression and rectification processes of the gas, on the one hand, the purity of CO2 in the raw material gas is required to be relatively low, and the present application is suitable for the liquefaction and purification of the low-purity CO2 flue gas mixture after the S / N / Hg integrated removal technology is applied to the oxygen-enriched combustion flue gas, on the other hand, the present application has the characteristics of low energy consumption and small circulating water consumption.

[0035] 2. The waste gas from the gas phase outlet at the top of the first flash separator enters the expander, and the expander can convert part of the internal energy of the waste gas into mechanical energy, so as to realize the utilization of the waste gas; the output end of the expander can be drivingly connected with the driving end of the first compressor, thereby further reducing the energy consumption of the device.

[0036] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments description will be briefly introduced. Obviously, the accompanying drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative effort.

[0038] Figure 1 Structure diagram of the CO2 purification device.

[0039] Icon:

[0040] VP1-Second flash separation device, V2-First throttle valve, VP2-First flash separation device, V1-Second throttle valve, E1-Heat exchanger,

[0041] C1-First compressor, C2-Second compressor, E3-Refrigerating unit, T1-Fractionating column, E2-Evaporator,

[0042] TE1-Expander, E4-Exhaust gas heater,

[0043] 101-Feed gas stream, 104-Stream of liquid phase outlet at the bottom of the second flash separation device, 106-Stream of liquid phase outlet at the bottom of the first flash separation device, 201-Stream of outlet of the first compressor, 205-Stream of gas phase outlet at the top of the fractionating column, 303-Stream of outlet of the expander. DETAILED DESCRIPTION

[0044] In the following, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the embodiments of the present application.

[0045] The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0046] Please refer to Figure 1 , in a first aspect, the present embodiment provides a CO2 purification device, which mainly can include a flash separation system, a compression fractionation purification system and an exhaust gas venting system, wherein the flash separation system mainly can include a heat exchanger E1 and a first flash separation device VP2; the compression fractionation purification system mainly can include a first compressor C1, a refrigerating unit E3, a fractionating column T1 and an evaporator E2; the exhaust gas venting system mainly can include an expander TE1.

[0047] The first flash separation device VP2 has a gas phase outlet at the top, a feed gas inlet at the middle and a liquid phase outlet at the bottom, and the gas phase outlet at the top of the first flash separation device VP2 is used to discharge exhaust gas.

[0048] The heat exchanger E1 can cool or reheat the streams in the device; in the present embodiment, preferably, the heat exchanger E1 is a heat exchange system composed of multiple plate-fin heat exchange units.

[0049] The first compressor C1 can pressurize the stream 106 from the liquid phase outlet at the bottom of the first flash separator; in the present embodiment, the first compressor C1 is provided with an inter-stage cooler (not shown in the figure) to reduce the inlet temperature of the second compressor C2 described below.

[0050] The refrigeration unit E3 uses ammonia as the refrigerant.

[0051] The rectification column T1 has a gas phase outlet at the top and a liquid phase outlet at the bottom; in the embodiment, preferably, the upper part of the rectification column T1 is not provided with a condenser, which is conducive to reducing energy consumption.

[0052] The evaporator E2 has a gas phase outlet at the top and a liquid phase outlet at the bottom, the liquid phase outlet at the bottom of the evaporator E2 is used to discharge the CO2 liquid product, and the gas phase outlet at the top of the evaporator E2 is in communication with the rectification column T1, and the stream from the gas phase outlet at the top of the evaporator E2 can enter the rectification column T1 as the ascending gas.

[0053] The expander TE1 can convert part of the internal energy of the gas into mechanical energy required for the rotation of the impeller through the impeller, and the rotating impeller can in turn drive other devices to act.

[0054] The gas phase outlet at the top of the first flash separator VP2 is in communication with the inlet of the expander TE1, the liquid phase outlet at the bottom of the first flash separator VP2 is in communication with the inlet of the first compressor C1, the outlet of the first compressor C1 is in communication with the inlet end of the refrigeration unit E3, the outlet end of the refrigeration unit E3 is in communication with the upper part of the rectification column T1, the liquid phase outlet at the bottom of the rectification column T1 is in communication with the evaporator E2, the gas phase outlet at the top of the evaporator E2 is in communication with the lower part of the rectification column T1, and the CO2 liquid product is discharged from the liquid phase outlet at the bottom of the evaporator E2; the raw gas stream 101 is first cooled and liquefied by the heat exchanger E1, and then enters the raw gas inlet in the middle of the first flash separator VP2; the stream 106 from the liquid phase outlet at the bottom of the first flash separator is first reheated by the heat exchanger E1, and then enters the compressor; the stream 201 from the outlet of the first compressor is first cooled by the heat exchanger E1, and then enters the rectification column T1.

[0055] In the present embodiment, the gas phase outlet at the top of the rectification column T1 is in communication with the raw gas inlet, and the stream 205 from the gas phase outlet at the top of the rectification column flows through the heat exchanger E1 to increase the yield of the CO2 liquid product.

[0056] In the present embodiment, the raw gas stream 101, as a heat source, first flows through the evaporator E2 for pre-cooling, and then enters the raw gas inlet after being cooled by the heat exchanger E1.

[0057] The flash separation system can further comprise a second flash separation device VP1, and the compressed rectification purification system can further comprise a second compressor C2; the gas phase outlet at the top of the second flash separation device VP1 is communicated with the raw material gas inlet, the liquid phase outlet at the bottom of the second flash separation device VP1 is communicated with the inlet of the second compressor C2, and the outlet of the second compressor C2 is communicated with the upper portion of the rectification tower T1. The second compressor C2 can be an intermediate gas charging compressor, or can be composed of two compressors for performing low-pressure stage and high-pressure stage compression respectively.

[0058] In the embodiment, preferably, the outlet of the first compressor C1 is communicated with the inlet of the second compressor C2, and the flow 104 of the liquid phase outlet at the bottom of the second flash separation device passes through the heat exchanger E1 and then is combined with the flow 201 of the outlet of the first compressor C1, and both of them enter the second compressor C2.

[0059] In the embodiment, the flow 106 of the liquid phase outlet at the bottom of the first flash separation device is provided with a first throttling valve V2, which is arranged in a cold insulation cold box (not shown in the figure) to perform throttling refrigeration on the flow 106 of the liquid phase outlet at the bottom of the first flash separation device; the flow 104 of the liquid phase outlet at the bottom of the second flash separation device is provided with a second throttling valve V1, which is arranged in a cold insulation cold box to perform throttling refrigeration on the flow 104 of the liquid phase outlet at the bottom of the second flash separation device.

[0060] The exhaust gas venting system can further comprise an exhaust gas heater E4, the inlet of the exhaust gas heater E4 is communicated with the gas phase outlet at the top of the first flash separation device VP2, and the outlet of the exhaust gas heater E4 is communicated with the inlet of the expander TE1. The exhaust gas heater E4 is arranged to prevent solidification of the gas entering the expander TE1.

[0061] In the embodiment, preferably, the flow 303 of the outlet of the expander passes through the heat exchanger E1 to recover cold energy.

[0062] In a second aspect, the embodiment provides a CO2 purification method, which adopts the CO2 purification device described above, and mainly can comprise the following steps:

[0063] The low-purity CO2 flue gas mixture is first compressed and dried to remove part of the pollutants and moisture, thereby forming a raw material gas with a pressure of 30 bar. The raw material gas obtained after compression and drying is first pre-cooled in an evaporator E2, then cooled and liquefied in a heat exchanger E1, and then sequentially passes through a second flash separator VP1, a first flash separator VP2, a first compressor C1, a second compressor C2, and a refrigeration unit E3. After being cooled and liquefied in the refrigeration unit E3, the raw material gas enters the upper part of a rectification tower T1. The liquid stream from the liquid phase outlet at the bottom of the rectification tower T1 enters the evaporator E2, and the CO2 liquid product is obtained from the liquid phase outlet at the bottom of the evaporator E2.

[0064] Wherein:

[0065] After the raw material gas enters the evaporator E2, it heats the liquid stream from the liquid phase outlet at the bottom of the rectification tower T1 as a heat source. Part of the liquid from the liquid phase outlet at the bottom of the rectification tower T1 is evaporated and enters the rectification tower T1 as an ascending gas.

[0066] The second flash separator VP1 separates the liquid phase and the gas phase at a temperature of about -24°C. The separated liquid phase is throttled and refrigerated by a first throttle valve V2, reheated by the heat exchanger E1, and then enters the second compressor C2. The separated gas phase enters the middle part of the first flash separator VP2.

[0067] The first flash separator VP2 separates the liquid phase and the gas phase at a temperature of about -54°C. The separated liquid phase is throttled and refrigerated by a second throttle valve V1, reheated by the heat exchanger E1, and then sequentially passes through the first compressor C1 and the second compressor C2. The separated gas phase is reheated by the heat exchanger E1 and heated by a waste gas heater E4, and then enters the expander TE1 to convert the internal energy of the waste gas into mechanical energy. The stream 303 at the outlet of the expander flows through the heat exchanger E1 to recover the cold energy.

[0068] The stream compressed by the second compressor C2 is first pre-cooled by the heat exchanger E1, then cooled and liquefied to about -10°C by the refrigeration unit E3, and then enters the upper part of the rectification tower T1 for rectification. Compared with the prior art, the refrigeration unit E3 of the present embodiment requires less cold energy and has lower energy consumption.

[0069] The stream 205 from the gas phase outlet at the top of the rectification tower is reheated by the heat exchanger E1 and then returns to the raw material gas stream 101, which enters the evaporator E2 together with the raw material gas.

[0070] The composition of the raw gas after compression and drying is shown in Table 1 below, and some calculation conditions under the basic working conditions at normal temperature and pressure are shown in Table 2. The pressure of the raw gas after compression and drying is 30 bar, and the heat loss, mechanical loss and pipeline pressure loss of the device are ignored. Under the condition that the volume fraction of CO2 in the raw gas is 76.6%, the parameters of the device are simulated and calculated, and when the purity of the CO2 liquid product is required to be 99.99%, the product yield can reach 90%.

[0071]

[0072]

[0073] From the above, the present application combines the flash separation of gas, compression and rectification process, compared with the prior art, on the one hand, the purity of CO2 in the raw gas is lower, which is suitable for the liquefaction purification of low-purity CO2 flue gas mixture after the S / N / Hg integrated removal technology of oxygen-enriched combustion flue gas, on the other hand, the device has the characteristics of low energy consumption and small circulating water consumption; in addition, the waste gas from the gas phase outlet of the top of the first flash separator enters the expander, and the expander can convert part of the internal energy of the waste gas into mechanical energy to realize the utilization of the waste gas; the output end of the expander can be drivingly connected with the driving end of the first compressor and the second compressor, so as to further reduce the energy consumption of the device.

[0074] Finally, it should be pointed out that: the above is only the preferred embodiment of the present application and is not used to limit the present application, for those skilled in the art, the present application can have various changes and variations, in the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other at will. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A CO2 purification apparatus, characterized in that, include: The system comprises a first flash separator, a heat exchanger, a first compressor, a refrigeration unit, a distillation column, an evaporator, and an expander. The heat exchanger is used to cool or reheat the stream in the CO2 purification device. The first flash separator has a raw material gas inlet in the middle. The gas phase outlet at the top of the first flash separator is connected to the inlet of the expander. The liquid phase outlet at the bottom of the first flash separator is connected to the inlet of the first compressor. The outlet of the first compressor is connected to the inlet of the refrigeration unit. The outlet of the refrigeration unit is connected to the upper part of the distillation column. The liquid phase outlet at the bottom of the distillation column is connected to the evaporator. The gas phase outlet at the top of the evaporator is connected to the lower part of the distillation column. The liquid phase outlet at the bottom of the evaporator is used to discharge CO2 liquid product. The upper part of the distillation column is not equipped with a condenser; The raw material gas stream first flows through the evaporator and then enters the raw material gas inlet of the first flash separator; The CO2 purification device also includes a second flash separator and a second compressor; The gas phase outlet at the top of the second flash separator is connected to the feed gas inlet of the first flash separator, the liquid phase outlet at the bottom of the second flash separator is connected to the inlet of the second compressor, and the outlet of the second compressor is connected to the upper part of the distillation column.

2. The CO2 purification apparatus according to claim 1, characterized in that, The feed gas stream first flows through the evaporator, then is cooled and liquefied by the heat exchanger, and then enters the feed gas inlet of the first flash separator; the stream from the liquid phase outlet at the bottom of the first flash separator is first reheated by the heat exchanger and then enters the first compressor; the stream from the outlet of the first compressor is first cooled by the heat exchanger and then enters the distillation column.

3. The CO2 purification apparatus according to claim 1, characterized in that, The vapor outlet at the top of the distillation column is connected to the feed gas inlet of the first flash separator; The stream from the vapor outlet at the top of the distillation column flows through the heat exchanger.

4. The CO2 purification apparatus according to claim 1, characterized in that, The outlet of the first compressor is connected to the inlet of the second compressor.

5. The CO2 purification apparatus according to claim 1, characterized in that, A first throttling valve is installed on the liquid phase outlet stream at the bottom of the first flash separator, and the first throttling valve is installed inside the cold box.

6. The CO2 purification apparatus according to any one of claims 1-5, characterized in that, The CO2 purification device also includes a waste gas heater; The inlet of the exhaust gas heater is connected to the gas phase outlet at the top of the first flash separator, and the outlet is connected to the inlet of the expander.

7. A method for purifying CO2, applied to the CO2 purification apparatus as described in claim 1, characterized in that, The purification method for CO2 includes the following steps: The raw gas obtained after compression and drying is first pre-cooled by an evaporator, then cooled and liquefied by a heat exchanger, and then sequentially passed through a second flash separator, a first flash separator, a first compressor, a second compressor, and a refrigeration unit. After being cooled and liquefied by the refrigeration unit, it enters the upper part of the distillation column. The liquid stream from the liquid phase outlet at the bottom of the distillation column enters the evaporator, and CO2 liquid product is obtained from the liquid phase outlet at the bottom of the evaporator. in: After the feed gas enters the evaporator, it acts as a heat source to heat the liquid stream from the liquid phase outlet at the bottom of the distillation column. Part of the liquid from the liquid phase outlet at the bottom of the distillation column is evaporated and then enters the distillation column as rising gas. The pressure of the compressed raw gas is 30 bar; The second flash separator separates the liquid and gas phases at a temperature of -24°C. The separated liquid phase is throttled and cooled by the second throttling valve, then reheated by the heat exchanger, and then enters the second compressor. The separated gas phase enters the middle part of the first flash separator. The first flash separator separates the liquid phase and the gas phase at a temperature of -54℃. The separated liquid phase is throttled and cooled by the first throttle valve, then reheated by the heat exchanger, and then passes through the first compressor and the second compressor in sequence. The separated gas phase is reheated by the heat exchanger and heated by the waste gas heater before entering the expander. The stream compressed by the second compressor is first pre-cooled by a heat exchanger, then liquefied to -10°C by a refrigeration unit, and then enters the upper part of the distillation column for distillation. The vapor stream from the top of the distillation column is reheated by a heat exchanger and then enters the evaporator together with the feed gas.

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